Recovery of oxygenated compounds from hydrocarbon oils



Sept. 25, 1951 c. E. MORRELL ETAL 2,569,385

RECOVERY OF OXYGENATED COMPOUNDS FRQM HYDROCARBON OILS Filed Feb. 12.1948 On PHASE ZONE wATaiLPHAsE 7N QAFFINflE Sana/grow.

5 Q SOLVENT EXTRACTION J 'ZONE ExTRAcT CPiar-Zes E. m -11 Janus 1-{ mgzgg Unveqtors bgMflbborneg Patented Sept. 25, 1951 RECOVERY OFOXYGENATED COMPOUNDS FROM HYDROCARBON oILs Charles E. Morrell,Westfleld, and James H. McAteer, Cranford, N. 1., asslgnors to StandardOil Development Company, a corporation of Delaware Application February12, 1948, Serial No. 7,966 Claims. (Cl. 260-450) This invention relatesto the recovery of the lower molecular weight oxygen-containing organiccompounds both neutral and acidic from mixtures thereof with hydrocarbonoils by a process involving the extraction of such mixtures with diluteaqueous solutions of the water-soluble car-' boxylic acids i. e. C1through Cs acids such as dilute aqueous acetic acid, dilute aqueouspropionic acid, etc., or mixtures of the same.

Various processes are knownto the art in which a mixture of hydrocarbonsand organic oxygen-containing compounds are produced. Some of theseprocesses are the low temperature carbonization of coal, peat andsimilar materials, the destructive hydrogenation and distillation ofcoals, wood, shales, etc. Numerous oxidation processes, particularlyoxidation of petroleum oil fractions, such as is described in EllisChemistry of Petroleum Derivatives, vol 1, chapter 36, pages 830 to 845,also yield mixtures of oxygenated compounds and hydrocarbons ofsubstantially the same boiling range. This invention is particularlyapplicable to the hydrocarbon syntheses, such as the Fischer synthesiswherein oxides of carbon are reacted with hydrogen in the presence ofcatalysts to produce synthetic hydrocarbons, water and numerous organicoxygenated compounds, predominantly aliphatic. The oxygenated compoundsproduced'in the synthesis operation may be a major product or arelatively small by-prodnot depending upon the operating conditions.These oxygenated materials which are extremely valuable as chemicals,consist of a mixture of alcohols, acids, aldehydes, ketones and estersand are diflicult to separate from thehydrocarobn oil because first,they are so numerous, secondly they boil within substantially the samerange as the hydrocarbon oils and, thirdly, they often form azeotropeswith each other and with the hydrocarbon oils.

Normally when the products of the above-described synthesis operationare condensed and allowed to settle, the condensate separates into adi-phase system, that is, an upper oil layer comprising substantiallyhydrocarbons and hydrocarhon-soluble oxygen-containing materials and alower water phase comprising substantially water and water-solubleoxygen-containing materials. The oxygen-containing organic compoundsformed in the synthesis operation range from very low molecular weightcompounds to very high molecular weight compounds and therefore findthemselves distributed throughout the oil phase and the water phasedepending on their solubilities in these respective phases. In general,it can be said that the bulk of the organic oxygen-containing compoundsof one of four carbon atoms will enter the aqueous phase while the bulkof the compounds containing five carbon atoms and more per molecule willbe found in the oil layer, although it should be borne in mind that theseparation of materials into their respective phases is oftentimes notclean-cut and depends to a large extent upon the conditions involved andthe overall composition of the materials in the condensate from thesynthesis reactor.

Processes have been developed for the separation and recovery ofalcohols, ketones, aldehydes, etc. from the water layer. The startingpoint in many of such'processes is a crude alcohol distillation in whichthe water layer is subjected to distillation to remove substantially allof the oxygenated compounds other than acids therefrom. Generallyspeaking, it is desired to leave the acids, such as acetic acid,propionic acid, etc., in the bottoms from which they are subsequentlyrecovered.

It is an object of this invention to provide a method for the recoveryof oxygenated compounds, particularly water-soluble oxygenated compoundsfrom mixtures thereof with hydrocarbon oils.

It is an object of this invention to provide a method for the recoveryof oxygenated compounds from the oil layer product of the hydrocarbonsynthesis.

It is also an object of this invention to provide a method for theseparation and recovery of organic oxygenated compounds both neutral andacidic from mixtures of both with hydrocarbon oils.

These and other objects of this invention are attained by carrying outthe extraction of a mixture of neutral and acidic oxygenated organiccompounds in hydrocarbon oils with a dilute aqueous solution of thewater-soluble aliphatic carboxylic acids, such as acetic acid, propionicacid, etc., 01' mixtures of such carboxylic acids, at a temperature inthe range of C. to the critical temperature of the solvent, preferably-250 C. The critical temperature of the solvent will be in theneighborhood of 375 C. The acid bottoms obtained from the fractionaldistillation of the synthesis water layer is especially suitable forthis extraction step as will be further explained below.

The material subjected to extraction, according to the terms of thisinvention, is complex in nature. It is composed of hydrocarbonsincluding paraflins, oleflns and in some cases, small amounts ofaromatics. In addition. it contains anywhere up to about 50% or more ofoxygencontain ing materials, particularly of high molecular weight suchas those set out above. In cases where the material is derived from thehydrocarbon synthesis operation. the oil will have dissolved in italcohols, acids, aldehydes, ketones and esters. Frequently, the esterspredominate among the high boiling compounds, particularly that fractionboiling above 350 F. while carbonyl compounds, that is aldehydes andketones, acids and alcohols, predominate among the oxygen containingcompounds boiling at temperatures up to about 350 F. Ordinarily theamounts of alcohols and acids found decrease with increasing analyticaldistillation temperatures due undoubtedly to the fact that they undergoesterincation reactions during such distillation treatments. The oxygencontent of the hydrocarbon oils resulting from the synthesis operationgenerally runs from one weight percent to ten weight percent.

It has been previously found, as described in our copending applicationSerial Number 792,802 filed December 19, 1947, that when such a mixtureof hydrocarbon oils and oxygenated compounds is extracted at lowtemperatures, 1. e. temperatures in the range of about C. to 125 C.,with a dilute aqueous solution of acetic acid with or without a smallamount of its homologues, the lower molecular weight neutral oxygenatedcompounds present in the mixture are extracted therefrom by the acidsolvent, leaving the lower molecular weight carboxylic acids containedin the mixture in the raflinate phase with the hydrocarbon oils. That isto say, the alcohols, esters, ketones, aldehydes, acetals, etc., throughC and some C6, are dissolved by the dilute aqueous acetic acid andconstitute the extract phase, while the acids present in the mixture areundissolved and together with the hydrocarbon oils in the mixtureconstitute the rafilnate phase.

However, it has now been found that when the hydrocarbon oil-oxygenatedcompound mixture is extracted with dilute aqueous carboxylic acids athigher temperatures, 1. e., in the range of 125 C. to the criticaltemperature of the solvent, both the neutral oxygenated compounds andthe acidic oxygenated compounds are extracted, leaving the raflinatecomposed chiefly of hydrocarbons and the higher molecular we ghtoxygenated compounds. Another feature of the high temperature extractionwith these acids is that at the higher temperatures, 1. e., 125 C. toabout 375 C., the esters pre ent in the hydrocarbon mixture aresubstantially hydrolyzed thus producing larger amounts of alcohols andacids in the extract phase.

The d lute aqueous carboxylic acid solution employed as the selectivesolvent according to the terms of this invention should contain no morethan 5 to weight percent of the acid. The preferred ran e is 2 to 5weight percent. The acid water bottoms previously described is an excelent solvent for the purpose of this invention.

The acid water bottoms obtained from the fract onal distillation of thesynthesis water layer contains about 95 weight percent water and atypical analysis is as follows:

Other org. oxy. compds. (alcohol, esters,

etc.) 0.03

The 4.4? weight percent acid content is broken down into approximatelyweight percent acetic acid, 20 weight percent propionic acid, and 5weight percent butyric acid and higher acids. The small amount of otheroxy-compounds present in the acid bottoms, i. e. the 0.03 weight percentalcohol, ester, etc., is not harmful to the material as a solvent.

In its simplest form this invention entails taking all or part of theaqueous acidic bottoms from the hydrocarbon synthesis water layer fromwhich substantially all of the alcohols, ketones, aldehydes, etc.,'havebeen removed and contacting the oil layer resulting from the synthesisproduct condensation with the aqueous bottoms under extractionconditions. The total oil layer or appropriate fractions thereof may beso treated. In a number of cases these bottoms may be used as such forthe extraction operation. This is especially true when it is desired toextract the oxygenated compounds from the lower boiling portions of theFischer synthesis oil, say for instance the gasoline fraction (up to 400F.). or some lower boiling portion of the gasoline fraction. Thisinvention also includes an alternate possibility in which a loweralcohol such as methyl, ethyl or isopropyl or mixtures of these loweralcohols or mixtures of these with other neutral oxygenated compoundssuch as ketones are added to the aqueous acidic bottoms and this mixtureemployed as the extraction agent. For instance, if the entire Fischersynthesis oil is to be extracted or if only the higher boiling portionsthereof are extracted, it is desirable that considerable amounts of thelower boiling oxygenated compounds be added to the aqueous bottoms inorder to obtain a suitable solvent for the extraction. Preferably,however, the amount of alcohols or other low boiling oxygenatedcompounds combined with the aqueous bottoms is kept at the lowest valueconsistent with reasonable capacity and selectivity of the extractionagent for the oil-soluble oxygenated compounds. Best results have beenobtained by the addition of at least 20 volume percent alcohol,particularly methanol.

The aqueous bottoms, eiher as such or after reinforcement with lowerboiling oxygenated compounds as described above, may be contacted.

with the oil or suitable fractions thereof under a variety ofconditions. For instance, the contacting may be carried out in a batchmanner. Preferably, however, it is carried out using countercurrent flowof the extractant and the oil, either in counter-stage equipment or in acountercurrent packed or plate tower. The optimum solvent to oil ratiowill vary over wide ranges depending upon the nature of the solvent, i.e. the

acid and lower boiling oxygenated compoundcontent thereof, theoxygenated compound con-' tent of the oil, the boiling range of the oilbeing extracted, and the temperature of the extraction. As theoxygenated compound content of the solvent is increased, the optimumsolvent/oil ratio, in general, decreases. Also, the lower the oxygenatedcompound content of the oil feed, the lower are the solvent/oil ratiorequirements. When extracting the higher boiling portions of the oil,either alone or in combination with the lower boiling portions thereof,in general, it is desirable to use a relatively high solvent/oil ratiosince the solubility of the higher boiling oxygenated compounds in suchaqueous solvents is lower than that of the lower boiling ones.

The temperature at which the extraction operation of this invention iscarried out is important.

lower than 125 C. are to be avoided when ex- 5 ti-acting the mixture ofhydrocarbons and oxygenated compounds with the dilute aqueou acidsolvents of this invention, due to the fact that at 1 the lowertemperatures, the acids contained in the mixture of hydrocarbons andoxygenated compounds are not extracted by the dilute aqueous acidsolvents, but remain instead in the railinate, thus making theseparation of oxygenated compounds incomplete. The preferred extractiontemperature range is 175 C. to 250 C.

The attached drawing represents a flow plan of'one process andaccompanying apparatus for carrying out this invention in its simplestembodiment.

Referring to the drawing, numeral i represents a reaction zone whichproduces a reaction product composed chiefly of hydrocarbons andoxygenated compounds, which when removed from the reaction andcondensed, form in vessel 2 an upper hydrocarbon oil phase and a lowerwater phase, each phase containing dissolved therein varying amounts oforganic oxygenated compounds such as alcohols, acids, ketones,aldehydes, etc., as explained previously. The water phase is removed vialine 3 to zone 4 which may be a fractional distillation zone, anextractive distillation zone or a solvent extraction zone for separationof the water layer oxygenated compounds into the water soluble neutraloxygenated compounds taken overhead via line 5, and the dilute aqueousorganic acids removed as bottoms via line 6. The oil phase from vessel 2is removed via line 1 to extraction zone 8 entering at a point below themid-section thereof. In extraction zone 8 the oil phase iscountercurrently extracted with all or part of the dilute aqueousorganic acid bottoms entering the extraction zone via line 9 at a pointnear the top thereof. During the extraction operation the lowermolecular weight oxygenatcd compounds both neutral and acidic in the oillayer are extracted bythe dilute aqueous acid and the resulting extractis removed for separation of solvent therefrom via line It). A raflinatephase is removed overhead from the extraction zone by line I I.

The extract phase consists substantially of the lower molecular weightorganic oxygenated compounds dissolved in the solvent. The oxygenatedcompounds can be removed from the solvent by any known means and thisinvention is not restricted to any method by which such removal isaccomplished. For example, the oxygenated extract phase to fractionaldistillation, extractive distillation, solvent extraction or other knownmethods of separation.

The raflinate phase from the extraction zone consists chiefly ofhydrocarbon oils and the higher molecular weight oxygenated compounds.After separation of the solvent from the rafiinate phase, the railinatemay be recovered for purification as gasoline, and/or further recoveryof the higher molecular weight oxygenated compounds. However, any suchtreatment is not within the scope of this invention.

In order to visualize the amount of C2-C5 oxygenated compounds presentin the synthesis oil layer, the following data are presented. In acertain hydrocarbon synthesis run the oxygenated compounds extracted bywater from the oil layer increases over the amounts obtained byprocessing the water layer from the same run.

Percent increase Propionic acid 15 Propyl alcoho 20 Butyric aci'd 100Butyl and amyl alcoho1s 600 The following table contains examples toillustrate the process of this invention. In the examples cited the feedto the extraction process was a gasoline fraction, B. P. 35-200 C.,recovered from a hydrocarbon synthesis unit. This gasoline contained thefollowing amounts of oxygenated compounds expressed in-ini1liequivalentsper gram: acids 0.70; alcohols 0.57; esters 0.25 and carbonyls 0.65. Thefeed was extracted with the acid water bottoms recovered from thehydrocarbon synthesis water layer stripped to remove volatile neutralcompounds therefrom. Analysis of the acid water bottoms revealed: acidcontent 4.2 weight percent as acetic acid; alcohol content 0.04 weightpercent as ethyl alcohol. those at room temperature.

Moi Per Cent Extracted Temp. Solvent] C. oil Ratio Ah can Aclds holsEsters bonyls l Room 0.07 -6 2 Room 0.50 -4 1.00 1 4 2.00 l 0.50 13 4.0061 1 Denotes loss of acid to raflinate phase, i. e., denotes an increasein amount of acids present in oil phase following extraction.

It will be observed that the acids are not extracted by the acid waterbottoms at room temperature, while at 250 C. the acid clean up isappreciable particularly at the higher solvent to oil ratio.Considerable increase in the amount of alcohols extracted is alsonoticeable and this is due in part to hydrolysis of esters at the higherextraction temperature aided no doubt by the acidic nature of theextraction solvent.

The solvent/feed ratios employed may be varied over a wide range andwill be determined in any particular case by the extraction temperature,the equipment employed and desired cleanup of the extractable oxygenatedcompounds.

- For most purposes, the optimum range of solvent compounds may berecovered by submitting the to feed ratio is from 2 to 5 to 1 althoughoperation at from about 0.25 to l to as high as 10 to 1 may be carriedout satisfactorily. By the solvent extraction process as described inthis invention all the oxygenated compounds containing up to andincluding five carbon atoms are quantitatively removed from the oillayer.

The removal of esters of C2 to C5 is more complete at the higherextraction temperatures of this invention due to hydrolysis. Inaddition,

incomplete removal of oxygenated compounds containing 6 carbon atoms andabove is also efl'ected. The higher molecular weight oxygenatedcompounds, i. e. those containing 6 carbon atoms and above, may be morecompletely {removed from the hydrocarbon oil by other methods not asubject of this invention.

As previously stated the higher extraction temperatures are conducive tothe substantial hydrolysis of esters present in the feed to theexrepresented the following approximate percentage 76 traction step.When the feed is known to con- The runs at 250 C. are contrasted withtain appreciable quantities of esters whose hydrolysis to more valuablealcohol and acid products is desirable the hydrolysis may be'acceleratedby the addition of small quantities of catalysts such as mineral acidsto the extraction solvent. The hydrolysis of esters is especiallypromoted by the presence of sulfuric acid or phosphoric acid inconcentrations up to 10 weight per cent in the solvent.

Although the invention has been illustrated by the use of dilute aqueousacid bottoms recovered from the hydrocarbon synthesis water layer, theinvention is by no means limited thereto. Dilute aqueous solutions ofthe water soluble aliphatic organic acids may be employed as well. Inaddition, the use of mixtures of the water-soluble aliphatic acids isalso included within the scope of this invention. For example, a diluteaqueous solution containing equal .or unequal proportions of acetic acidand propionic acid, or acetic acid and butyric acid may be employed.

Having fully described the invention in a manner such that it may bepracticed by those skilled in the art,

What is claimed is:

1. An improved process for the recovery of aliphatic oxygenatedcompounds containing 1 to 6 carbon atoms per molecule from a mixture ofsuch oxygenated compounds with hydrocarbons of substantially the sameboilin'g range, said mixture resulting from the catalytic hydrogenationof oxides of carbon, which comprises selectively extracting theoxygenated compounds from the mixture in a liquid-liquid extraction bycontact with a dilute aqueous solution of acetic acid, containingapproximately 2 to 5 weight percentage of acetic acid, at a temperaturein the range of 125 C. to 375 C., separating an extract phase comprisingthe oxygenated compounds and a raflinate phase comprising thehydrocarbons, and recovering the oxygenated compounds from the extractphase.

2. A process according to claim 1 in which the extraction is carried outat a temperature between 175 C. and 250 C.

3. A process according to claim 1 in which the ratio of solvent to feedextracted is between 0.25 to 1 and to 1.

4. An improved process for the separation of aliphatic oxygenatedcompounds from hydrocarbon oil solutions containing them produced asreaction products in a hydrocarbon synthesis reaction whereby oxides ofcarbon are hydrogenated in the presence of a catalyst to yield a productwhich when condensed, separates into a hydrocarbon oil phase containingdissolved oxygenated compounds and an aqueous phase containing dissolvedoxygenated compounds, which comprises separating the hydrocarbon oilphase from the aqueous phase, fractionally distilling the aqueous phaseto produce an overhead product comprising essentially neutral oxygenatedaliphatic compounds, and an aqueous bottoms containing 2- to 10 weightpercent aliphatic carboxylic acids containing less than 5 carbon atomsper molecule, contacting the hydrocarbon oil phase at a temperaturebetween 125 C. and 375 C. with said aqueous bottoms containing 2 to 10weight percentage aliphatic carboxylic acids containing less than 5carbon atoms per molecule, separating an extract phase comprising thoxygenated compounds, and a rafiinate phase comprising the hydrocarbons,and recovering the aliphatic oxy; genated compounds from the extractphase.

5. A process according to claim 4 in which the low molecular weightoxygenated compounds contain from 1 to 6 carbon atoms per molecule.

6. An improved process for the separation of neutral and acidicaliphatic oxygenated compounds from hydrocarbon oil solutionscontaining' them produced as reaction products in a hydrocarbonsynthesis reaction whereby oxides oi carbon are hydrogenated in thepresence of a catalyst to yield a product which when condensed separatesinto a hydrocarbon oil phase and an aqueous phase, which comprisesseparating the hydrocarbon oil phase from the aqueous phase. contactingthe hydrocarbon oil phase in a liquidliquid extraction at a temperaturebetween C. and 375 C. with a dilute aqueous carboxylic acid containingless than 5 carbon atoms per. molecule and containing 2% to 10% byweight of acid, separating an extract phase comprising the neutral andacidic oxygenated compounds and a rafllnate phase comprising thehydrocarbons, and recovering said oxygenated compounds from the extractphase.

7. An improved process for the separation and recovery of aliphaticoxygenated compounds comprising alcohols, aldehydes, ketones, esters,-acetals, and acids from a mixture of such oxygenated compounds withhydrocarbons which comprises extracting the oxygenated compounds. fromthe mixture in a liquid-liquid extraction by. contact with a solventcomprising a dilute aqueous solution of an aliphatic carboxylic acidcontaining less than 5 carbon atoms per molecule and containing 2% to10% by weight of acid, at atemperature between 125 C. and 375 C.,separat-a ing an extract phase comprising the aliphatic oxygenatedcompounds and a rafllnate phase comprising the hydrocarbons, andrecovering the aliphatic oxygenated compounds from the extract phase.

8. A process according to claim 7 in which the oxygenated compounds arecontained in a mix-' ture with hydrocarbons of substantially the sameboiling range.

9. A process according to claim 7 in which the aliphatic oxygenatedcompounds contain from 1 to 6 carbon atoms per molecule.

10. A process according to claim 7 in which the solvent is aqueous acidbottoms containing 2% to 10% by weight of acid recovered from the waterlayer of a hydrocarbon synthesis reaction product.

CHARLES E. MORRELL. JAMES H. MCATEER.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,452,121 Grahame Oct. 26, 19482,472,219 Lyons June 7, 1949 2,476,788 White July 19, 1949 OTHERREFERENCES

1. AN IMPROVED PROCESS FOR THE RECOVERY OF ALIPHATIC OXYGENATEDCOMPOUNDS CONTAINING 1 TO 6 CARBON ATOMS PER MOLECULE FROM A MIXTURE OFSUCH OXYGENATED COMPOUNDS WITH HYDROCARBONS OF SUBSTANTIALLY THE SAMEBOILING RANGE, SAID MIXTURE RESULTING FROM THE CATALYTIC HYDROGENATIONOF OXIDES OF CARBON, WHICH COMPRISES SELECTIVELY EXTRACTING THEOXYGENATED COMPOUNDS FROM THE MIXTURE IN A LIQUID-LIQUID EXTRACTION BYCONTACT WITH A DILUTE AQUEOUS SOLUTION OF ACETIC ACID, CONTAININGAPPROXIMATELY 2 TO 5 WEIGHT PERCENTAGE OF ACETIC ACID, AT A TEMPERATUREIN THE RANGE OF 150* C. TO 375* C., SEPARATING AN EXTRACT PHASECOMPRISING THE OXYGENATED COMPOUNDS AND A RAFFINATE PHASE COMPRISING THEHYDROCARBONS, AND RECOVERING THE OXYGENATED COMPOUNDS FROM THE EXTRACTPHASE.